Jon Jones vs. Daniel Cormier -- Fighters Brawl At Promo Event

Jon Jones and Daniel Cormier couldn't wait until September 27 to fight ... so they brawled Monday in the middle of the MGM in Las Vegas ... and this one didn't look fake at all.

Jones and Cormier got nose-to-nose, which Cormier was not into ... so he shoved Jones away. Clearly Jones was not pleased, so he went after Cormier and the two knocked the backdrop over before tumbling off the stage.

The two went at it on Twitter afterwards, with Cormier writing, "I won't let another man get in my face and put his forehead against mine. I will react every time. @jonnybones next time i will slap you"

For his part, Jones wrote, "yo, DC you suck. you suck. you gonna chop me over the neck and get beat up - And I had you on your back - what - in 6 seconds - you suck. you felt so weak."

UFC 178 is gonna be awesome!